1. Field of the Invention
The present invention relates to an antenna device and a communication apparatus including the same, and more specifically, the present invention relates to an antenna device and a communication apparatus including the same for use in mobile communications or the like.
2. Description of the Related Art
With a recent advance in miniaturization and high performance of mobile communication devices, particularly in those of mobile phones, an antenna device, which is to be mounted therein, has also been required to be further miniaturized and to have higher gain.
FIG. 5 and FIG. 6 show a conventional surface-mount type antenna and an antenna device incorporating the same, respectively. The basic structure of the surface-mount type antenna 1 shown in FIG. 5 is described in Japanese Unexamined Patent Publication No. 9-98015.
In FIG. 5, the surface-mount type antenna 1 is arranged by disposing some electrodes on a surface of a base member 2 of a rectangular parallelepiped configuration, which comprises a dielectric material such as ceramic or resin as one of the insulation materials. First, a ground electrode 3 is disposed on substantially the entirety of one major surface 2a of the base member 2. In addition, a strip-shaped radiation electrode 4 is disposed along the length direction of the base member 2 on the other major surface 2b of the base member 2. One end 4a of the radiation electrode 4 extends onto one end surface of the base member 2 to form an open-circuited end and the other end 4b extends onto a major surface 2a and over another end surface of the base member 2 to be connected to the ground electrode 3. Furthermore, a power feeding terminal 5 is disposed in the vicinity of the end 4a of the radiation electrode 4 on the end surface on which the end 4a of the radiation electrode 4 of the base member 2 is disposed. In this arrangement, the power feeding terminal 5 extends over the end surface of the base member 2 to the major surface 2a to be insulated from the ground electrode 3.
In an antenna device 6 incorporating the surface-mount type antenna 1 shown in FIG. 6, a mounting substrate 7 includes a substrate 8 comprising a dielectric material, i.e., an insulating material, having a major surface 8a, another major surface 8b, a substrate-ground electrode 9 disposed on the other major surface 8b and a power feeding line (not shown) which is insulated from the substrate-ground electrode 9. The surface-mount type antenna 1 is mounted on the substrate-ground electrode 9 in the vicinity of a corner of the mounting substrate 7. In this arrangement, the ground electrode 3 and the power feeding terminal 5 of the surface-mount type antenna 1 are connected to the substrate-ground electrode 9 and the power feeding line, respectively, on the mounting substrate 7 by soldering or the like.
In order to achieve miniaturization of a communication apparatus in which an antenna device has been mounted, miniaturization of the antenna device, i.e., reduction in the cubic volume taken by the surface-mount type antenna on a mounting substrate, is required. Thus, the effort required for making the surface-mount type antenna itself smaller is considerable. When the surface-mount type antenna 1 shown in FIG. 5 is miniaturized, the entire size of the base member 2 of the surface-mount type antenna 1 must be made smaller. However, with a surface-mount type antenna, there is a tendency in which the smaller the size of the base member, the smaller the antenna gain. Accordingly, miniaturization in the size of the base member 2 of the surface-mount type antenna 1 permits the antenna gain of the surface-mount type antenna 1, i.e., the antenna gain of the antenna device 6, to be reduced.